This application pertains to the art of valves and, more particularly, to valves for use on vehicle air brake systems. The invention is particularly applicable for use on tractor-trailer air brake systems and will be described with particular reference thereto. However, it will be appreciated that the invention has broader aspects and the valve may be used in other systems.
Tractor-trailer air brake systems commonly include a shutoff valve between the tractor and trailer lines for shutting off flow of service air from the tractor service line to the trailer service line when the trailer is not connected, or when the trailer emergency line breaks. The shutoff valve is normally moved to an open position for establishing flow between the tractor and trailer service lines by pressure supplied to the valve from the tractor emergency line. Subsequent to a brake application, air bleeds from both the tractor and trailer service lines through the foot control valve. Bleeding the air from the trailer service line back to the foot control valve delays complete release of the trailer brakes.
One valve of the type described for tractor-trailer air brake systems is disclosed in U.S. Pat. No. 3,183,919 issued May 18, 1965, to Herring. Examples of combined shutoff and exhaust valves include those disclosed in U.S. Pat. Nos. 2,816,563 issued Dec. 17, 1957, to Pappas and 3,428,071 issued Feb. 18, 1969, to Kobnick. These valves do not incorporate a positive shutoff operable in accordance with the pressure in the emergency line. In addition, the structure of the valves is relatively complicated.